I need help

Jenni • So in Love with my perfect man since 4*20*2014
Not sure where to post this but if someone can tell me how to fix this.
So about 7 years ago my grandma got me a phone for Verizon in her name but I was paying the bill. I canceled it before the 2 year contract was up. They said I would have a early cancellation fee of about $300. I said that fine. My phone got stolen as well but it was just a cheap phone so I didn't really care   Well Verizon is fucking up my grandmas credit and still trying to charge her $1000s of dollars even 7 years later. What can I do?